Minimale Levensvatbare Populaties: Een uitwerking voor populaties zandhagedissen, Lacerta agilis, en levendbarende hagedissen, Lacerta vivipara, in Nederland

Within ecosystems species disappear and species emerge. The number of species within a system fluctuates because of migration and dispersion. During the last century human interventions on natural systems increased. Because of the intensification of agriculture, industrialisation and urbanisation populations are threatened with extinction. This is mainly caused by habitat degradation and habitat fragmentation. Therefore it is important to get an insight in the threshold value of the population size at which the population is able to survive. Threatened species can be prevented from extinction as long as their population size does not drop below their threshold value. The biogeographic theories of MacArthur and Wilson served as a basis for the concept of the Minimum Viable Population size. To estimate the Minimum Viable Population size either the genetic approach can be used or the approach based on demographic and environmental stochasticy. The genetic approach calculates a minimum population size of 500 individuals. A population size of 500 individuals or more will be able to survive in the long term. The approach of demographic and environmental stochasticy does not give an exact number of individuals, because this differs per species and situation. This report presents the calculations of the potential capacity of the present occupied patches in The Netherlands of 34 populations of the sandlizard (Lacerta agilis) ) and of 36 populations of the viviparous lizard ( Lacerta vivipara). The potential capacity is analysed with the use of the genetic approach of the Minimum Viable Population theory. When the number of individuals, which could be present (potentially) in a patch, is below the threshold value of 500 than the patch is classified as too small and/or qualitatively unsuitable. For 6 patches of the sandlizard the potential capacity was below 500 individuals. For all investigated patches of the viviparous lizard the potential capacity was far above 500 individuals.