Sunday, April 18, 2010

Invaders of Missouri

At my co-editor's urging, we are starting an Invaders of Missouri series.  She was pushing for an Invader of the Month but I am not that organized.  Before we get started, a few definitions from Wikipedia are in order.
  • Invasive Species- non-indigenous species, or 'non-native' plants or animals that adversely affect the habitats and bioregions they invade economically, environmentally, and/or ecologically.
  • Naturalized species - any process by which a non-native organism spreads into the wild and becomes naturalized. A population is said to be naturalized if its reproduction is sufficient to maintain it.
  • Exotic Species- (introduced, alien, exotic, non-indigenous, or non-native species) is a species living outside its native distributional range, which has arrived there by human activity, either deliberate or accidental. 
Now it gets complicated.  Recall that an exotic is generally a species that is native to one area and displaced to another.  As you can see, an exotic species that becomes naturalized is a potential invasive species looking for a place to happen.  Frequently it just needs the right biological niche such as a lack of predators or competition, or a particular unique biologic skill which allows it to out compete its new neighbors.  Some of these skills in plants are below.
  • Early blooming, seed production and rapid growth, allowing a plant to shade out competing plants.
  • High volume of seed production with efficient dispersal mechanisms.  Each flower head of a Musk Thistle produces thousands of feathered seeds capable of broad wind dispersal.
  • Deeper taproot systems tapping into scarce water resources.
  • Wide range of habitats and tolerance (alkaline soil, acidic soil, shade and sun tolerance, etc.)
  • Reproduced by seed or vegetative reproduction- above ground or below ground “runners” (stolons and rhizomes)
  • Allelopathic chemicals that inhibit the growth of near by plants.  Tree of Heaven is notorious for producing ailanthone which is reported to possess non-selective properties similar to glyphosate (Round Up) and paraquat.  Some native species, such as Black Walnut which produces juglone, use this strategy as well.
  • Bad taste which deters animals from eating it.  Sericea lespedeza has high tannin levels which make it less palatable to both livestock and insects which then eat other neighboring plants.
It is unclear why plants native to one area are so much more aggressive when they go on a foreign vacation and decide to stay there, but it may be related to coevolution, a concept first proposed by Darwin.  As plant and animal species evolve they adapt ways to share available resources.  They may develop strategies to overcome allelopathic chemicals, develop the tools to eat otherwise indigestible plants or otherwise evolve a strategic parity with its neighbors over thousands of years of living together.  When they are suddenly in a totally new place, none of their neighbors know how to handle them.
Over the next year we will be covering current invaders- from the vicious to the early, possible future concerns.  My goal is to provide a source of convenient online resources to identify and attack the Invaders of Missouri.

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