Shameless Self Promotion: Effective non-invasive genetic monitoring of multiple wild western gorilla groups

Photo by Josephine Head of a Loango gorilla

My collaborators and I have a paper that just came online which shows that by using scat samples, collected over a 100 square kilometer area in Loango National Park, Gabon, we could obtain individual genetic fingerprints (genotypes) from most of the gorillas there. We then used those genotypes to assess the number of gorillas living in the area, as well as the grouping patterns of the individuals, their ranging area and even some dispersal events between groups. Methods and results like these are an important first step in devising proper conservation management policies for great apes. Despite all the amazing work that has been done on chimpanzees and gorillas, we still do not have a good idea of how many are left in the wild, nor where they range and we don't have very good methods with which to obtain these measures. With repeated genetic sampling over years, we will be able to look at changes in ape number as well as track individual animals over whatever area is sampled. -MA

Arandjelovic M, Head J, Kühl H, Boesch C, Robbins MM, Maisels F, Vigilant L (2010) Effective non-invasive genetic monitoring of multiple wild western gorilla groups. Biological Conservation doi:10.1016/j.biocon.2010.04.030

Abstract
Obtaining reliable population size or abundance estimates of endangered species is critical for their conservation and management. Genotyping non-invasively collected samples is an effective way to gain insights into the number and grouping patterns of rare or elusive animals. In this study we used genetic capture–recapture estimators to obtain a precise estimate of the size of a western gorilla population inhabiting an intensely sampled 101 km2 area in Loango National Park, Gabon. Using 394 putative gorilla samples collected opportunistically over a 3 year period, we identified 83 unique genotypes. We used a rarefaction curve, Bayesian estimator and two maximum-likelihood methods to estimate that between 87 and 107 individuals used the study area between February 2005 and September 2007. The confidence interval surrounding the genetic estimate was smaller than that obtained using traditional ape survey methods. In addition, genetic analysis showed that gorilla and chimpanzee faeces were identified with 98% and 95% accuracy in the field, respectively. Patterns of co-occurrence of individual gorillas suggest that at least 11 gorilla social groups and five lone silverback males lived in the study area and that several individuals transferred between groups during the 3-year study period. When properly designed and implemented as part of a long-term biomonitoring program, genetic capture-recapture should prove an invaluable tool for evaluating, even on a large-scale, the population size and dynamics of apes and other elusive species.

For a copy of the pdf, click here