ENV 217 Bioinvasions and Forest Decline

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ENV 217Bioinvasions and Forest Decline
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Evolution in Reverse

• We are in the throes of a vast and
  little-noticed biotic upheaval. As ecological
  entities, the continents are coming together the
  seas are spilling into each other. And this
  biotic turmoil is reaching levels of disturbance
  that no actual meeting of rock or water could
  possibly achieve. Modern commerce is wrapping
  the worlds natural systems in a web of
  connections that is far more comprehensive than
  anything that could have existed on the ancient
  super-continent. A type of hyper-Pangaea is
  emerging
• Chris Bright Life out of Bounds, Norton 1998

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The success of the portmanteau biota and its of
its dominant member, the European human, was a
team effort by organisms that had evolved in
conflict and cooperation over a long time. The
success overseas of this biota was a
multispecies revolution whose aftershocks still
rock the biosphere.
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Bioinvasion represent a major threat to
biodiversity

• Ranks just behind habitat loss as a global
  extinction threat.
• Estimated that bioinvasion has been a factor in
  68 of fish extinction.
• Invasions often result in functional extinctions,
  e.g Melaleuca a tree invading the Everglades
  reduces diversity from 60-80 in a wet prairie to
  2-3 species

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Rule of tensAs a general rule 10 of exotics
will become established. 10 will launch a major
invasion.
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Typically the exotic species takes many years to
establish itself before becoming a major pest
More unknown about exotic species than is
known Which organisms will become pests? Where
will invasions occur? Disturbed habitats? When
will the invasion occur? What will the impact be?
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Characteristics of Invadible Habitats

• Lowered biotic resistance - disturbed soil, bad
  grazing practice etc.
• Communities of undefended prey - where natural
  predators go extinct or do not exist there is
  increased vulnerability to invasion islands are
  classic example.
• Habitats without invaders specialized predators -
  e.g purple loosestrife.
• Habitats with established invaders that
  facilitates new invaders - pigs and strawberry
  guava in Hawaii.

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Ecological Consequences

• Generalized supercompetition
• Niche usurpation
• Generalized superexploitation
• Specialized superexploitation
• Habitat modification

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Causes of Invasions

• Deliberate introductions crops, ornamentals,
  landscape modifiers.
• European Botanic gardens importing plants from
  colonies.
• Accidental introductions Dutch Elm Disease,
  Chestnut blight, Asian long-horn beetle etc.

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Consequences

• Replacement of diverse system
• Direct threats to natives by habitat change
• Alterations of soil chemistry
• Alterations of geo-morphological processes.
• Plant extinction by competition
• Alteration of fire regime
• Alteration of hydrological conditions