Posted by: oikosasa | February 1, 2013

The elephant in the room

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What makes invasive species invasive? Find some of the answers in Rafael Zennis and Martin Nunez paper “The elephant in the room: the role of failed invasions in understanding invasion biology”  now on Early View.

Here, Martin Nunez gives a short background:

Invasive species grow bigger, reproduce earlier and more often, and spread faster than other species, right? Well, sometimes yes, but not always. Many known invasive species have populations introduced in areas where they do not naturalize or invade after arrival. As it turns out, only invasive populations exist in nature. In this study, we reviewed the literature on invasions and found that failures are the most numerous and often ignored part of the biological invasion process. We learned that very few people are interested in introduced populations that do not thrive in the new environment. There are many anecdotal reports on failures, but really few studies on why these populations fail. We also found that different mechanisms may be causing failures vs. successes, but more research is needed to shed light on this. Based on these findings, we show and discuss research areas where it may be key to incorporate more info on failures to avoid an important bias.

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Maritine pines (Pinus pinaster) are invasive in many parts of the southern hemisphere, but in Rio Negro, Brazil, experimental plantations died out 18 years after planting leaving no trace of its past presence in the area, now colonized by exotic eucalyptus and native araucaria pines.

We focused our study on reviewing cases of species that are invasive somewhere, but that fail to invade in other areas, habitats or time periods. We did this because these situations can provide useful information on the particular mechanism of invasion (e.g., what is different between areas where the species invade and where the species does not invade?). We avoided studying species that never invaded, which might provide little information about other invasive species.  Finally, we put caution in the use of the term “invasive” to indicate an intrinsic species-level trait because even some of the most aggressive invaders are reportedly unable to colonize some area. This does not change, however, the fact that when introduced organisms do invade, they may cause considerable changes in community and ecosystem dynamics.

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