Higher altitude of islands increases their number of exclusive species

Oceanic islands are born, they grow, they are eroded and they disappear beneath the sea. Throughout this process, which takes millions of years, the islands change form and therefore change their 'tenants'. The species adapt to the new environmental conditions, occupy empty niches, specialise and become exclusive. In the case of the youngest islands with high mountainous ecosystems, the endemic ecosystems increase.

"After reaching their maximum height, the island's topography is at its most complex due to erosion and it also has its highest level of biodiversity," José María Fernandez-Palacios, ecology professor at La Laguna University said. He highlighted that when islands have high mountainous ecosystems, they have more exclusive species.

A study which Fernández-Palacios has co-written, and has been published in the journal Ecography, reiterates the role of altitude in explaining an island's exclusive biodiversity. This, like age and other factors, affects the diversity amongst species.

The double isolation that affects species in highly mountainous conditions makes them unique. The research team shows that the highest islands create conditions that increase the number of endemisms.

"These higher mountainous island ecosystem species have evolved habitually from species that occupy the lower or middle areas of the islands in question. They are island species that have to adjust to very specific and rare ecosystems" Fernández-Palacios affirms. According to the researcher, high mountain area in Tenerife consists of less than 10% of the island's surface and La Palma has around 1%.

'Move' from the island or die

"On islands that are more topographically complex, these species would not exist because the high mountain is the first to disappear from an island when it is eroded" Fernández-Palacios notes. La Gomera and Gran Canaria do not have high mountains because they are more than 10 million years old, but they had them in the past. Actually high mountains have an important role in younger islands, like La Palma.

Nonetheless, despite having "older and wrinklier" relief, La Gomera has more biodiversity than La Palma "because it has many exclusive ravine or hillside species." "La Palma is simpler, taller and bigger, but not so complex" the scientist affirms, who points out that despite that, it has many high mountain species that "surely" came from La Gomera.

As the island is eroded, the high mountain species have two options. "If the nearby island is tall enough, they "leap" to this new territory and they survive there. If it has not reached an appropriate height, the species' ecosystem becomes extinct" the researcher points out.