Predicting tick distributions in a changing climate: An ensemble approach for South Africa

Predicting the potential distribution of disease vectors is crucial for vector management and disease transmission surveillance. This study aims to assess changes in the geographic projection of the ecological niche of ticks of veterinary, public health, and economic importance in South Africa, and to predict areas suitable for their establishment under current and future climate scenarios. We used a suite of six algorithms within the ensemble modelling framework of the biomod2 package in R version 4.4.2 to produce species distribution models for current (2021-2040) and future (2041-2060) climate scenarios. Six bioclimatic variables, representing a range of biophysical and anthropogenic factors, were used in combination with tick presence-only occurrence data submitted to SANBI's Integrated Publishing Toolkit by tick species experts. The model outputs indicate that all 10 tick species will likely experience range shifts over time (2021-2060). All species are projected to gain significant portions of suitable ranges in the future. Notably, Rhipicephalus microplus is predicted to gain the most, with a 14 % increase in its suitable range in South Africa. This predicted range expansion could potentially disrupt ecological balances in the ecosystems it is likely to occupy. Native species such as Amblyomma hebraeum and Hyalomma rufipes are predicted to expand their ranges by 10 and 9 %, respectively, while others may gain less than 6 % of their potential ranges The overall predicted range expansion could also introduce new disease dynamics, potentially leading to increased pathogen transmission, host switching and higher incidences of diseases in humans and animals in currently unaffected areas. The study provides baseline information to support ongoing monitoring and adaptive management strategies to mitigate the negative impacts associated with ticks on ecosystems, public health, and agriculture. The results will help inform tick control programs in South Africa and other similar environments. South Africa must adopt a comprehensive One Health approach to tick management to address the challenges posed by invasive species like R. microplus, which threaten livestock health and have significant veterinary and economic impacts.