These differ in part considerably from the propagation strategies of endemic plant species. Dr. Ingolf Kühn and Dr. Sonja Knapp of the Helmholtz Centre for Environmental Research (UFZ) reached this conclusion in a study published in the current issue of the scientific journal Ecology Letters.
"These results are an argument in support of the view that the need to differentiate between native and non-native species in ecological systems remains", says Dr. Ingolf Kühn.
Experts are currently debating whether this differentiation might be untenable, as it is only a question of the extent to which a plant species - regardless of its origin - is able to adapt to man-made conditions (Davis et al. (2011), Nature; Thompson et al. (2011) Trends in Ecology & Evolution). In the professional journal Trends in Ecology & Evolution (van Kleunen et al. (2011), Hulme et al. (2011)) a number of research groups counter with the argument that differentiating between these two groups contributes essentially to the understanding of modern ecosystems, as endemic and non-native species differ in many respects.
In their current study the UFZ researchers Dr. Ingolf Kühn and Dr. Sonja Knapp investigated this thesis and examined the question, whether the factors influencing the frequency of occurrence of non-native plant species are different from those for native species. Their investigations made use of the BiolFlor biological-ecologic data base for the characteristic features of flora in Germany, with more than 3,600 native and also established introduced species of ferns and flowering plants. They compared such features as life span, pollinating strategy and the occupation of different habitats and relate these features to the frequency of occurrence of a particular species.
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 with the native species. It is therefore understandable that newly arrived plants occupy niches not completely used by native species. Consequently, such non-native species frequently make use of these niches. Most introduced species pose no serious threats to our ecosystems. Around one per cent of the introduced species are, however, invasive. This means that their spread is so significant that they suppress native plants and disturb the ecosystem.The UFZ researchers therefore believe that the differentiation between native and non-native plant species remains correct and important, even when they have been established in Germany for many centuries. Dr. Ingolf Kühn: "On the evolutionary time scale 500 years are a mere blinking of an eye. And because native and introduced species in fact exhibit differences in certain features, they should not all be considered together. Especially the importance of the early recognition of possible dangers due to the presence of introduced species requires knowledge of their origin."
The investigations were supported by the the Helmholtz Association (core subject ‘Land Use Options and Biodiversity').Additional scientific information:
http://www.ufz.de/index.php?en=21942At the Helmholtz Centre for Environmental Research (UFZ) scientists are researching the causes and consequences of far-reaching changes to the environment. They are concerned with water resources, biological diversity, the consequences of climate change and adaptability, environmental and biotechnologies, bioenergy, the behaviour of chemicals in the environment, their effect on health, modelling and social science issues. Their guiding theme: Our research contributes to the sustainable use of natural resources and helps to secure this basis for life over the long term under the effects of global change. The UFZ employs 1,000 people in Leipzig, Halle and Magdeburg. It is financed by the federal government and the federal states of Saxony and Saxony-Anhalt.
http://www.ufz.de/The Helmholtz Association contributes towards solving major and pressing social, scientific and economic issues with scientific excellence in six research areas: Energy, Earth and Environment, Health, Key Technologies, Structure of Matter, Aeronautics, Aerospace and Transport. The Helmholtz Association is Germany's largest scientific organisation with over 33,000 employees in 18 research centres and an annual budget of approximately 3.4 billion euros. Its work stands in the tradition of the naturalist Hermann von Helmholtz (1821-1894).
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