Monitoring and predicting elusive species colonisation – Application to the otter in the Cévennes National Park (France)

Abstract:

The movements of some wildlife species are secretive and the process of change in their population distribution is often poorly documented. The objective of this research is to develop an integrative approach to monitor and predict the colonisation of elusive species. The study focuses on the Eurasian otter (Lutra lutra L.) in the mid-mountainous landscape of the Cévennes National Park (France). Statistical analyses of 15-years field survey, GIS-modelling and non-invasive genetics are combined to (1) optimise the species detection; (2) define a relevant framework for data analysis; (3) retrace the settlement chronology; (4) get genetic information about colonisers; and (5) predict the spatial process of colonisation.

Findings were both methodological and specific to otter ecology. Looking for spraints, i.e. otter faeces, along riverbanks, we showed that one long (> 5.5 km) or multiple short surveys (e.g. 13 x 50 m) were necessary to predict otter presence with 95% efficiency in a basin at a colonisation front. The marking density and frequency were relevant indicators of the settlement process. An original modelling approach validated the use of functional distances from detection places to predict otter occurrence where it was not detected, which may contribute to address the issue of ‘false-absences’. By this method, we retraced the time sequence of colonisation at the basin scale showing a mean rate of about 10 km / year. Extraction and analysis of DNA from spraints were used as the only efficient technique to better understand the population distribution dynamics (73% PCR amplification success; 98% genotyping reliability; 0.6% probability to obtain an identical genotype among relatives). 70 individuals were genotyped describing the population along 1650 km of rivers. Sex ratio was 57% males. Individual movements were observed up to 60 km. Two genetic clusters were identified (Fst: 0.102) partially separated by watershed lines. Assignment tests demonstrated that rivers and marshy passes between valleys were colonisation paths and that steep ridges (> 8° on average) were effective barriers.

Combining different advanced tools in a multidisciplinary approach proved to be efficient in inferring animal movements from indirect signs only. Such approach should be used with population dynamics models in order to predict space and time status changes of elusive and vulnerable species.

Please contact me (janssensx@yahoo.fr) if interested for the full text - PDF (included publications are still “submitted” or “in press”).

Sincerely,

Xavier Janssens
PhD from Université catholique de Louvain
Unit of Environmetry and geomatics