Talk, FloraMac 2015, Gran Canaria, Spain: 2015-03-24 - 2015-03-27
Abstract:
High elevation islands (HEI), especially in the tropics and subtropics, are global hotspots of plant diversity. Owing to their isolation and strong environmental gradients their exceptional position in terms of diversity results in large parts from in-situ speciation, leading to the evolution of endemic species. Thus, understanding the underlying drivers of diversity and the disturbances that shape them may offer fundamental insights into general ecological processes. In this study I assess (a) which environmental drivers (esp. topography and climate) determine the distribution of endemic richness, endemicity (percentage of endemics) and endemic rarity, and (b) how globally relevant disturbances (introduced herbivores, fire, roads) affect endemic diversity. I use the HEI La Palma (Canary Islands) as a model system, where our workgroup recorded endemic species in almost 1000 plots and used fenced exclosure established by the NP Caldera de Taburiente in 2000 in the high elevation ecosystem. Topography mainly determined endemic richness, while climate was most important for endemicity and endemic rarity. This indicates that spatially decoupled diversity hotspots exist, which has important implications for conservation management. A combination of eco-evolutionary processes and anthropogenic influences shape the current distribution of endemic diversity on La Palma. Introduced herbivores have a strong negative impact, whereas fire seems to positively affect high elevation plant diversity. Massive conservation efforts are needed to preserve highly threatened endemics in the high elevation ecosystem, including large fenced exclosures and population control of introduced herbivores. Surprisingly, roads have a positive effect on endemic richness, probably because rupicolous endemics are adapted to roadside cliff conditions and are protected from other anthropogenic disturbances. Owing to the continental-scale environmental gradients on the landscape scale of a medium-sized oceanic island, it is justifiable to call La Palma a climatic mini-continent, highlighting that the insights gained here are relevant for other non-insular systems.