Predicting the potential distribution of an invasive ant species, Wasmania auropunctata in Israel

Potential distribution and monitoring the invasive species “The little fire ant” (Wasmannia auropunctata)
Roy Federman and Yohay Carmel

The Little Fire Ant (Wasmannia auropunctata) is an invasive species that originates in South and Central America and it is among the 100 most damaging invasive species as defined by the IUCN. Over the past century, this species invaded many areas around the world, including Israel. The monitoring method used to identify newly infested sites in Israel has not been evaluated for efficiency and lacks defined conditions for execution. The main objectives of this study are to predict W. auropunctata potential distribution at the global and local (Israeli) scales and to improve the monitoring method of this species. W. auropunctata’s potential distribution was predicted using a model for species distribution called MAXENT. Model input data included species location records within the native range and climatic variables. The model output is a map which assigns a value for potential establishment for each pixel relative to other pixels within the model extent. Invasive records were used to evaluate the performance of the models. Climate variables were obtained from online datasets. These datasets do not account for water input due to irrigation. I corrected this gap by adjusting precipitation data to express actual water input in these areas. This correction improved the performance of the global and local models, demonstrating the importance of water input in determining the distribution of this species. Improvement in the global model prediction occurred in five different geographical regions; a result which demonstrates the importance of irrigation correction for various geographical and climatic regions. Globally, areas of high establishment potential were distributed mainly within the equatorial climate zone. The local model predicted high establishment potential in the transition between semi- arid and Mediterranean climate zones as well as in irrigated lands within the Mediterranean zone. The global and local models were compared for the area of Israel, and showed high agreement between them, even though they were based on different datasets at different scales. Within Israel, currently the species does not utilize the full range of its potential niche and is expected to further spread to suitable habitats, mainly to irrigated lands. This study also sought to improve monitoring within Israel by defining the optimal survey methodology in this region. Current methods, which include bait placement and direct searching, were tested using field observations and experiments. The following parameters were tested: bait density, microclimate conditions at occupied bait locations and optimal weather conditions for performing surveys. In addition, I compared the efficiency of the bait and direct search methods. Direct searching was found as the recommended monitoring method for sites with known infestation, supplemented by baits placed in locations that humans can not effectively observe. Baits were found to be more effective in shaded sites. Surveys are most effective when performed on summer mornings. For discovering new infestations, I recommend direct searches in combination with baits placed at 1m intervals. By identifying areas of high W. auropunctata establishment potential and improving current monitoring methodologies, this study allows managers to more effectively monitor and prevent the spread of this invasive species.

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