Monitoring population viability
Work in this area by Alterra focuses on studying fragmented and isolated populations.
The number of individuals in these populations is often too low to ensure vitality and mating between related individuals can occur, which leads to loss of genetic variability. Therefore, information about genetic variability is important for instance in assessments of critical population sizes, or breeding and/or (re-)introduction programs for endangered species. However, molecular tools can not only be used to study levels of genetic variability in populations, but also to reveal population characteristics such as number of individuals, dynamics (turnover and dispersal), kinship, etc. This is very important because most endangered animal species are elusive and night active, and therefore hard to study by conventional demographic methods.
Examples monitoring population viability
Monitoring the reintroduction of the otter in the Netherlands
The reintroduction of the otter (Lutra lutra) into the Netherlands has been accompanied by a monitoring programme. Traditional techniques like telemetry were supported by non-invasive DNA typing of otter spraints (droppings). The power of the DNA method is that individuals can be identified for a longer period after release, more individuals can be covered, while limited fieldwork efforts and costs are required. Since July 2002, 31 otters have been released and over a thousand spraints have been collected. DNA was extracted and analysed at our laboratory to obtain genetic fingerprints. In this way, individuals could be tracked in the field, and their relationships could be investigated. Based on these data we were able to map territories and dispersal and to produce a pedigree of the population. This allowed us to estimate the size of the (breeding) population and to show that inbreeding levels are rising quickly. This information shows that further management is required to prevent future problems.
Captive breeding and restocking of the Common hamster
Intensive agricultural practices recently brought the Common hamster (Cricetus cricetus) to the brink of extinction in the Netherlands. In 1999, 15 of the last remaining hamsters were caught for a captive breeding programme. Agricultural reserves have been created, where captive bred hamsters have been released successfully since 2002. A genetic study was conducted to estimate genetic diversity in the populations and to identify the most suitable donor population for increasing the gene pool of the breeding stock. We revealed that whereas the historical Dutch population (as inferred from museum specimens) was related to hamsters in Belgium and in the German border area, the current population shows very low genetic variability and is highly differentiated from other populations. This has clear consequences for future management.
Conservation status of the Black grouse
Major habitat destruction was the main cause of the large reduction in numbers of Black grouse (Tetrao tetrix) in the Netherlands. Currently only a small population of birds survives in the Sallandse Heuvelrug area, with the nearest populations more than 200 kilometres away. Despite conservation measures such as enlarging the habitat, basic predator control and controlled tourism, the population still shows no sign of increasing. To ascertain whether the population was suffering from inbreeding depression, a genetic study was conducted to determine the genetic variability and differentiation compared to the population that existed in the past (based on museum specimens) and populations from elsewhere in Europe. Like for the hamster, the results indicated that in the past the Dutch grouse population was closely related to foreign reference populations, but that the remaining Dutch population has lost genetic variability and has drifted away from other populations. Genetic techniques were also used to study the number of individuals involved in mating.