The Use of DNA to Estimate Population Sizes in Cambodian Elephants

This project was carried out by Fauna & Flora International (FFI), who collected over 500 dung samples from forests in Cambodia. Elephant DNA was extracted using polymerase chain reaction (PCR). Eighteen genetic markers plus a sex marker were used in an attempt to identify individual elephants. Each marker yielded one or two alleles, although “allelic drop-out” often resulted in one or both alleles being unidentified.

To overcome these short-comings in the data, BioEcoSS Ltd. used two computer-intensive methods to provide useful population estimates. Firstly, to identify real alleles from the "PCR noise", a genetic algorithm was developed to model the clusters of base-pair measurements, resulting in 94% of all B-P values contributing to the subsequent analysis. Secondly, pair-wise comparisons, utilising Monte Carlo simulations, were used to deduce the probability that any two samples came from the same elephant. In this way, it was possible to extract the maximum information from otherwise limited data to give estimated ranges of minimum number alive with acceptably narrow confidence limits.