Trophic niche of invasive murid rodents in urban and peri-urban areas in South Africa : insights from stable isotope analysis

Abstract

There are three invasive Rattus species (R. norvegicus, R. rattus, R. tanezumi) that are known to occur in South Africa. The three Rattus species are widespread in urban and peri-urban areas where they have had a significant impact on human health, infrastructure, and biodiversity. There is, however, limited information on their trophic ecology and on how factors that affect access to, and utilization of, food resources facilitate successful establishment. This study applied stable isotope analysis (SIA) to assess the trophic niches of the three Rattus species across selected urban and peri-urban landscapes in Gauteng Province. The three Rattus species occurred allopatrically: R. norvegicus in urban areas (Alexandra and Tembisa townships), R. rattus in the peri-urban University of Pretoria Experimental Farm, and R. tanezumi in peri-urban areas near Hammanskraal. Rattus tanezumi and R. rattus exploited broader food resources in peri-urban areas that are used for agricultural activities, while R. norvegicus had a more restricted niche in urban environments. Niche breadth expanded in summer, reflecting seasonal food availability, while sex- and age-related differences suggested subtle differences in feeding strategies, although the results were inconsistent across species and sites. Although some limitations, such as the fact that the three Rattus species were sampled in allopatry and missing baseline resources constrained interpretation, the study provides insights into how invasive rats adapt to different environments. Future research combining stable isotope analysis with long-term monitoring data will be essential to clarify niche partitioning and guide effective management of invasive rat populations.