The monitoring of genetic diversity is essential for the proper protection of endangered plants and animals in the Netherlands. This is the conclusion of Paul Arens, a researcher at the Plant Research International institute at Wageningen UR. Arens received his doctorate at the University of Groningen in December 2005 for his thesis on genetic variety. Among other things, Arens’s study found that, while there is very little diversity within isolated populations of the European tree frog, differences between populations are considerable. Since high diversity in a species has a positive effect on its resilience, this insight is crucial if adequate measures are to be taken to protect endangered plants and animals.
While numerous plants and animals are threatened with extinction in the tropics, the Netherlands also has its endangered species. These are registered in so-called Red Lists, official inventories of endangered plants and animals in the Netherlands. The species on the Red Lists are not automatically protected, which would require an adaptation of the Flora and Fauna Law.
The most efficient way of protecting endangered plants and animals is conscious landscape management. Protection of the environment, the extension of nature areas and targeted management all enlarge and improve natural habitats. Isolated populations of plants and animals can be brought back into contact with each other by linking separate areas via connecting zones, wildlife viaducts, badger tunnels and the like.
Most isolated populations of plants and animals suffer from a loss of genetic variety, which can be remedied to a certain extent by linking them to each other. In the long run, higher diversity ensures better adaptability to changing environmental circumstances by these species and reduces the risk of extinction. In addition, increased variability has a direct and positive effect on offspring size.
In his research, Arens concentrated on two animal and three plant species, namely the European tree frog, the moor frog, the black poplar, the May lily and the wood sedge. The genetic diversity of each of these species showed effects of human interference with the environment.
The area around Borculo (in the Dutch Achterhoek region) where Arens studied the European tree frog still had tens of thousands of tree frogs at the beginning of the last century. Human interference reduced this number to around a hundred by the 1970s. A conservation programme was started at the end of the 20th century aimed at improving the conditions of the European tree frog, among other things by reconstructing ponds and thickets. This has led to a gradual recovery of tree frog populations in this area.
Arens showed that the genetic diversity of tree frog populations within clusters of closely grouped ponds was extremely limited. The differences were, however, considerable between pond clusters. This indicated that different aspects of the original diversity have been preserved within each pond cluster and that the populations have had little or no contact with each other since then.
Arens compared the genetic diversity of his frogs with that of European tree frog populations in Denmark. This showed that the Danish populations were more genetically diverse than the Dutch ones, despite strong indications that the loss of genetic variety in the Danish populations had already led to increased offspring mortality. Arens therefore concluded that the Dutch populations are even more vulnerable than the Danish ones, and that further loss of diversity has to be prevented.
International research into, among others, wolves and vipers has shown that the (temporary) introduction of individuals from other populations in threatened groups leads to higher genetic variation within the target population, increasing its fitness. This was proved by various factors, including a sharp increase in the number of offspring.
Arens therefore concludes that monitoring of genetic variety, possibly linked to the introduction of individuals from more diverse populations, is extremely important for the protection of endangered plant and animal species. "Simply improving and linking natural habitats will not be sufficient," he writes. "We cannot make a serious contribution to the preservation of endangered animals and plants without measuring the genetic diversity of endangered species and increasing it with various activities, such as the introduction of individuals. This is especially important now that endangered species are also confronted with the additional threat of climate change."