Browsing by Author "Ulbrich, Ruben"

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    Utilization and distribution of selected invasive alien species in Germany and Namibia in comparison to the areas of origin
    (2015) Ulbrich, Ruben
    Leucaena leucocephala (Lam) de Wit, Prosopis L. spp, Prunus serotina Ehrh. and Robinia pseudoacacia L. originated in North America but are invasive alien species in different parts of the world. The aim of the study was to determine the actual and possible species distribution of Leucaena leucocephala and six Prosopis spp in Namibia as well as Prunus serotina and Robinia pseudoacacia in Germany. Species distribution modelling, using the software Maxent, was employed to predict the distribution of each species in the host region and to compare the actual and possible distribution according to the growing conditions of the donor region. Three different models were used. Model 1 included occurrence points and the ten most important environmental variables of the donor region. Model 2 used the same ten most important environmental variables but from the host area and Model 3 was calculated only with data of the host area. Occurrence points were obtained from the local herbarium, the GBIF database and road counts. Environmental variables consisted of different soil and climate variables. The results of the study calculated significant differences between the maps of Model 1 and 2, while Model 3 produced almost similar results to Model 2. The contribution of each variable to the model differed between the three models. Model 3 used three to five new variables. Response curves of each variable for univariate models showed different effects on the occurrence probability for each species. All species used a smaller range of environmental conditions in the host area compared to the donor region. The available and rarefied occurrence records and the time gap between species introduction to the rapid spread may explain the differences found in Models 2 and 3 in comparison to Model 1. The study demonstrated the importance of modelling invasive alien species with donor and host data in order to avoid wrong conclusions and underestimation of the potential threat of invasive alien species. Additionally, actual and reliable occurrence records are essential for accurate mapping predictions; regular monitoring and more intensive studies of invasive species especially in Namibia are necessary to accurately predict their range and impacts on native ecosystems.