Exotic grass will only invade when a grassland is JUST RIGHT

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Goldilocks and the Three Bears is a surprisingly informative story about biological invasions. A little girl breaks into a house (invades if you will) and she would have just cleared off if only hot porridge and hard furniture were offered. But instead she found food and a bed that were just right….so she stuck around.  

Similarly, when an exotic species rocks up to a new area they are confronted with a recipient community that will have both favorable and unfavorable conditions. Invasion will be either facilitated or inhibited by properties of that ecosystem.

But ecosystems are complex, and communities will have many properties that have direct and indirect effects of varying strengths. For example, what if Goldilocks found the appropriate porridge but there wasn’t any chairs or beds in the whole house that were just right. Would she still stick around (read: successfully invade)?

That’s kind of what Pappa-bear Sam and his family of researchers were interested in determining within the context of grasslands in Rush Valley, Utah. In this full-factorial experiment, Bromus tectorum (exotic annual grass) plays the role of Goldilocks, with disturbance and biotic resistance being those properties of the grassland (food and furniture of the house) that need to be just right.

In short, what they found was Bromus was unable to invade unburnt grassland (disturbance was required to remove those competitively dominant natives), and even if a grassland was burnt, invasion was still inhibited if there were abundant rodents (these consumers were providing the community with biotic resistance).

However, where a grassland had been burnt, and these rodents experimentally removed, Bromus invasion was a go! Densities increased exponentially to more than 1200 stems per square meter. These findings clearly demonstrate the importance of the interaction between disturbance and biotic resistance in facilitating or inhibiting invasion of this community.

For the actual science of this story, you should definitely read the paper and contact the authors if you have any questions.

St. Clair SB, O’Connor R, Gill R & McMillan B (2016) Biotic resistance and disturbance: rodent consumers regulate post-fire plant invasions and increase plant community diversity. Ecology DOI:10.1002/ecy.1391 [early view]

K!E#19 by Luke S. O’Loughlin

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