Quantifying the invasion probability of genetically modified plants

Abstract An operative and quantitative methodology for assessing the ecological risk of a GMP invading a natural habitat is presented. The suggested method evaluates whether dispersal to a specific habitat may take place and calculates the predicted probabilities of establishment, using information on dispersal and Bayesian statistics on data from simple competition experiments. Additionally, the method allows evaluation of the probability that a native species goes locally extinct in the invasion process. Keywords: Genetically modified plants, GMP, GMO, Invasion probability, risk assessment. Introduction of new species or genotypes to an area may be an irreversible process. If a plant is introduced into a natural habitat it may be impossible in practice to remove it again. Therefore, it is important to make an assessment of possible ecological risks of genetically modified plants (GMP) before they are released for commercial growing. Here, the particular ecological risk of a GMP invading a natural habitat and possibly out-competing a native plant species will be discussed. In risk assessment, a risk normally is defined as the probability that a specific event will occur multiplied by the negative impact of the event (Risk = Probability x Impact) (Vose, 2000, Damgaard and Lokke, 2001) . Thus, a risk assessment is separated in two parts; quantification of the probability that a specific event will occur, and quantification of the negative impact of the event. The negative impact of a specific ecological scenario, e.g. extinction of a native species, has to be quantified by the public or the decision-makers who will experience the reduced biodiversity. Note that humans and not ecosystems perceive an ecological risk. If the public is not concerned whether a specific species (including its unique role in the functioning of the ecosystem) goes extinct, then the negative impact and consequently the risk is zero. Ecological systems are complex, so in the ecological risk assessment we have to concentrate on the most important factors that control the invasion of plants into a specific habitat. The term invasion is used in different ways in the ecological literature. Normally, the invasion process is thought of as a series of steps from the establishment phase (the species is present), to the naturalisation phase (the population can maintain itself), and finally the invasion phase (the species can spread to other areas) (e.g., Williamson, 1996). However, if we aim at quantifying the invasion process we have to be more precise than merely to speak of a capacity to spread to other areas, since the invasion probability will depend on the plant community structure at the area. It is useful to define the invasion process for specific habitats as a local increase in plant density from non-existent to a density where the population can maintain itself (e.g., Bolker, et. al., 2000) . The probability that a GMP invades a specific natural habitat may be defined as the