DIFFICULTIES IN DETERMINING DISTRIBUTION OF POPULATION SIZES WITHIN DIFFERENT ORCHID METAPOPULATIONS.

When examining the probability of extinction of a given orchid species, the species must be viewed as a metapopulation composed of many individual populations connected by migration. In biology, much attention has been paid to the dynamics of metapopulations, especially in the situation where metapopulation dynamics are affected by active migration of individuals between populations. However, this is not the case with orchids. Their seeds are passively spread by wind, and therefore are unable to actively choose the point where they land (passive migrants, unlike, e.g., butterflies, which can actively look for a suitable site that hosts, hosted or can potentially host a population of their species (active migrants). Thus, while active migrants can often find a suitable destination for their migration, passive migrants often die after landing at an unsuitable site. One would therefore expect that, other things being equal, the proportion of suitable sites inhabited by active migrants is larger than that inhabited by passive migrants. In passive migrants (orchids) we may therefore meet metapopulation dynamics of a different, yet unexplored type, in which some existing localities die out and new localities appear, in the vast majority where no orchids have ever grown before. This type of dynamics has not yet been studied anywhere and this paper is intended to be the first step in this direction. The main goal here is therefore empirical determination of actual distributions of population sizes in different metapopulations. We do it in four regions of the Czech Republic and for four species of orchids, considering the factors that influence it. [ABSTRACT FROM AUTHOR]