A study of IMEDEA (UIB-CSIC) and the Meteorology Research Group at the UIB highlights the climate change effects on the Mediterranean tortoise

tortuga mediterráneaResearchers at the Mediterranean Institute for Advanced Studies (CSIC-UIB) and at the University of the Balearic Islands have shown in a scientific study that a shift to a more arid climate would have negative consequences for population persistence, the improvement of juvenile survival, and would increase risk of quasiextinction of the Mediterranean tortoise (Testudo hermanni) due to a decrease in the recruitment rate.The article, published on the Global Change Biology journal and featured on its October issue cover, points out that these processes may change depending the population and the climate scenario considered, but the results indicate that unless other sources of mortality induced by man are suppressed (i.e., poaching, fires, habitat fragmentation), climate variability increases the risk of extinction in most populations of this species. As Albert Fernandez Chacon, predoctoral researcher at the IMEDEA (CSIC-UIB) and first author of the publication, explains “in this study we examine the consequences of changes in precipitation and temperature expected for southern Europe in the population dynamics of the threatened (and endemic) Mediterranean tortoise (Testudo hermanni), in order to generate significant results for conservation measures consistent with climate change.”

Climate and population dynamics

The analysis of capture-recapture data collected between 1988 and 2009 (20 years) in the Ebro Delta allowed the calculation of survival rates and the evaluation of the effects of climate variability observed over the years on the local survival of the turtles.

The scientific study found that the amount of winter rainfall affected the annual survival of juvenile turtles. This relationship between climate and survival was used in a simulation conducted by the Meteorology Research Group at the UIB to predict the future of this population using 3 possible future climate scenarios (dry, wet and intermediate). This exercise was repeated with ten other turtle populations studied at other locations in southern Europe (from Spain to Greece) to produce a map of extinction risk that encompasses the entire geographical distribution of the species.

The results showed that under the dry scenario, the extinction risk is compounded by a lack of recruitment (the incorporation of new breeding individuals in the population). However, the study detected different degrees of risk across the species’ distribution area due to local differences in precipitation and presence/absence of non-climatic disturbance (predators, fires, illegal harvesting). The greatest risk of extinction was obtained for locations where the climate models predicted very dry winters and where there were additional factors besides mortality resulting from the existence of non-climatic disturbances.

Climate change is considered a threat to medium-long term for many animal populations. However, the relationship between climate and future population dynamics remains unexamined in many endangered species as climate changes are spatially heterogeneous and difficult to predict. So concludes Fernández Chacón, “this research will enable managers to design management strategies for the species taking into account the forecasts of local climate change, helping in making decisions about the most appropriate conservation measures for each species in the population.”

The study has been funded by the Ebro Delta Natural Park (Government of Catalonia), the Ministry of Science and Innovation, the Council for Research and Technological Innovation (CIRIT) and the MEDICANES research project.



Albert Fernández-Chacón, Albert Bertolero, Arnau Amengual, Giacomo Tavecchia, Víctor Homar and Daniel Oro; Spatial heterogeneity in the effects of climate change on the population dynamics of a Mediterranean tortoise. Global Change Biology doi: 10.1111/j.1365-2486.2011.02469.x

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