Niche change analysis as a tool to inform management of two invasive species in Eastern Africa

Significant progress has been made in providing guidelines and recommendations for assessing theecological niche, stage of invasion, and probability of invasive alien plant species (IAPS) potential distribution inspace and time. We followed these recommendations by developing and comparing ordination and species dis-tribution models (SDMs) of two important woody IAPS in Eastern Africa,Prosopis julifloraandLantana camara,and interpreting the results to inform IAPS management. The two species differ in their invasion history in East-ern Africa; whileL. camarawas widely introduced there in the 19th century,P. juliflorawas only planted atselected locations in the 1970s and 1980s. For the SDMs, machine learning algorithms were used to generate oneensemble model each forP. julifloraandL. camara. For ordination, we used bioclimatic variables, performed aprincipal component analysis, and compared the native and global niches of the species with the Eastern Africanniche. Niches varied substantially depending on the percentage of marginal climates excluded from the models.Additional analysis ofthe local niches surrounding the originalP. julifloraplantations showed that they are com-plementary, which may have led to anoverestimation of regional nichefilling. While niche expansion was absentor small depending on the percentage of marginal climates excluded, analysis of the stages of invasion suggestedthatP. julifloramay have started to adapt to novel climatic conditions and thatL. camarais approaching apseudo-stable equilibrium in Eastern Africa. The SDMs showed that large areas in Eastern Africa that have notyet been invaded byP. julifloraare suitable or will become suitable with climate change. ForL. camara,theglobalSDM predicted a considerably larger suitable area than the Eastern African one, raising uncertainty about theareas to be included in a regional management strategy. Thus, combining ordination and SDMs and integratinga geographic component into ordination is useful in assessing IAPS invasion stages and potential niche shifts,and the results help inform IAPS policy and management. The combined approach can also serve to guideexperimental studies addressing divergences betweenresults generated with the different approaches.