Contrasting effects of invasive rabbits on endemic plants driving vegetation change in a subtropical alpine insular environment

Abstract

Alpine ecosystems on islands are among the most isolated on Earth, leading to very high rates of endemism. Endemic species on oceanic islands are particularly vulnerable to invasive herbivores. In the alpine zone of Tenerife, which harbors a unique endemic flora, the dominance pattern of the two most dominant species in our days (Spartocytisus supranubius and Pterocephalus lasiospermus) has shifted in the last few decades, which may be a result of increasing rabbit pressure. In this study we explore how rabbits affect the population structure, soil nutrient composition and regeneration of our two target endemics within Teide National Park. For this purpose, we established 90 plots at 30 locations. Within 13 locations we sampled permanent exclosure plots that were established between 7 and 12 years before sampling, applying three treatments (full herbivory, rabbit herbivory and no herbivory). At one site we collected 80 soil samples to evaluate changes in soil chemistry and plant growth using a greenhouse experiment. Our results show that rabbits have a negative effect on the population structure of S. supranubius, while the contrary occurs with P. lasiospermus. Rabbit presence alters soil chemistry leading to a decline in nitrogen, which affects growth in both species. The presence of rabbits leads to a dominance shift in these two keystone endemic species, altering dominance patterns in the summit scrub of Tenerife. The decline of S. supranubius could represent the example of many endemic species of this system. Thus, we call for an immediate control of rabbit population (< 0.5 rabbits/ha) to protect this unique alpine endemic flora.