Their results show that the frequency of occurrence of the introduced plant species is in fact influenced by other strategies than the frequency of occurrence of native species. "The introduced species profit in particular from the fact that they blossom later in the year. The flowering time is, on the other hand, not a relevant feature for the frequency of occurrence of native species", says Dr. Sonja Knapp. A number of the most common introduced plant species seek a time niche between October and December, during which most of the native competitors no longer blossom. The remaining pollinators, such as bees, bumble bees and certain other insects, then pollinate only these plants. If there are no longer sufficient pollinators during this time, many of the introduced plants, such as asters and other composite flowers, can undergo self-pollination and in this manner ensure their survival.
For many native species an advantageous strategy is to become well established in many different habitats, such as in forested areas and simultaneously in meadows. "On the other hand, for non-native species this appears to be less important. They do not need to occupy as many different habitats as the native species in order to achieve the same frequency of occurrence", says Dr. Sonja Knapp. The introduced plant species are so successful in the few habitats in which they occur that widespread adaptation is no longer necessary. This is probably related to the origin of many non-native plants in Germany: The successfully introduced species are above all species which have adapted to an agricultural environment, which accompany seeds or have the character of field herbs, or species able to adapt to disturbances such as found in urban habitats, and which therefore have good possibilities for spreading over large areas.
Non-native plant species are, initially, in competition wit
|Contact: Tilo Arnhold|
Helmholtz Association of German Research Centres