Antagonist effects of rabbits on endemic plants as drivers of the vegetation changes in subtropical high mountain insular environments

Trabajo presentado en el II International Conference on Island Evolution, Ecology and Conservation, celebrado en Angra do Heroísmo, Islas Azores (Portugal) del 18 al 22 de julio de 2016.
The European rabbit, Oryctolagus cuniculus, is an invasive mammal in the Canary Islands and a keystone species in alteration of island ecosystems worldwide. It may dramatically affect the vegetation through different mechanisms, and therefore contribute to modifying habitat and communities, producing benefits in some species and damaging others. Thus, the rabbit might be considered as an ‘ecosystem engineer’. Through a study on the population structure of the endemics shrubs Spartocytisus supranubius and Pterocephalus lasiospermus, we explored the role of rabbits as a keystone in driving changes on dominant species of the summit vegetation of El Teide National Park (Tenerife, Canary Islands). We also analysed the spatial heterogeneity of these two dominant species, their relation with the herbivores, the plant age-classes and the growth response to variation in soil nutrient availability. For these purposes 90 plots were established at 30 localities within the high mountain area. Furthermore, we used 13 permanent plots in two types of herbivore exclusions (‘only big-herbivores’ and ‘all herbivores’). In one of the localities, 100 soil samples were collected to analyse the relationship between changes in nutrients (N, NO3, K) produced by rabbits and plant growth. The population of S. supranubius is clearly declining due to the negative effect of rabbits in its regeneration, matching with a rapid increase in the population of P. lasiospermus. This study also showed that the density of rabbits is the most influential variable affecting the population structure of S. supranubius. Furthermore, the increase in nitrates and potassium favour the growth of P. lasiospermus. The high contrast in palatability between both species and the different response to the increase in nitrates and potassium, represent the main forces in explaining the current dynamic of the vegetation in the high mountain of Tenerife. Our results highlight the urgency to control the great density of rabbits in this area.