The Current High Bird Colonisation Rate in a Major Mediterranean Island is Consistent With a More Intense Past Defaunation Compared to Nearby Mainland

Aim

We expand here previous own biogeographic work on the determinants of avian colonisation of a major land-bridge Mediterranean island. So far we have explained mechanistically the high current rate of colonisation of the island which proceeds by overflow of mainland species with growing population trends and with prior experience as winter visitors. However, here we focus on the historical factors that have led to such a high colonisation rate.

Location

Majorca Island and a nearby Iberian mainland coastal region with equivalent characteristics (Alicante province).

Time Period

Twenty-five years (1991–2015).

Major Taxa Studied

Birds.

Methods

We compared the pattern of species gain and loss in Majorca and Alicante during the study period.

Results

We found that while Alicante only gained eight new species and lost one, Majorca lost none and gained 21 species as breeders (odds ratio 2.6). The process of species gains in 5-year periods since 1991 showed a nonlinear pattern in both regions, with an abrupt decline in Alicante starting in 2006–2010 and final stagnation during 2011–2015, but just a smooth and recent pattern of slowdown in Majorca (2011–2015 on). Taxonomic diversity of colonising species at the family level, as well as habitat of colonisation, were quite similar between regions, but larger body size species were more common in Majorca.

Main Conclusions

We conclude that current differential colonisation rates between both regions are consistent with a more intense past defaunation of the resource-poor region (Majorca) prior to modern rural flight that happened simultaneously in both regions. While Alicante could be approaching a theoretical carrying capacity in the number of species, Majorca is farther from it. We predict that the island will continue gaining species in the next few decades. Worldwide, further research on comparing wildlife recovery rates between regions with differential intensity of past wildlife defaunation is badly needed to understand biodiversity recovery processes.