Biology and anthropology of plant invasions - Invasive Plants: Ecological and Agricultural Aspects - page 221

ice melting and exposing a terrestrial habitat. What would the first higher plant
invaders look like? Imagine that humans colonize Mars. What will their con-
trolled environment plant communities look like? In either case, does there
now exist plant traits that may provide answers to these two speculative ques-
tions? Would exploitation of the traits that allow invasive species to succeed
provide us with better plant communities? Whether Antarctic, Martian, agri-
cultural or scenic?
As humans alter the earth's habitats directly and indirectly, some consider-
ation should be given to preserving and exploiting the germplasm of our best-
adapted invasive and weedy species for such a future. Preservation of weedy
and invasive genotypes is an emerging issue in science as novel and unique
weedy biotypes are lost with the significant changes biotechnological crop
introductions are causing [e.g., 15, 16]. The traits these noxious plants possess
may provide novel solutions to the problems we create in expanding human
communities. The only obstacle to utilizing invasive plants as sources of novel,
useful traits in crops for biotechnology is our perception of what is useful,
beautiful and harmful.
Other ecological services are provided by weeds and invasives. Purple
loosestrife ( Lythrum salicaria ) is a beautiful and pleasing plant species. Zebra
mussels ( Dreissena polymorpha ) have cleaned turbidity from many localities
in the US great lakes (e.g., Michigan's Saginaw Bay and Lake Huron), enhanc-
ing human health and recreational value. Weeds are a major food source for
indigenous wildlife bird and animal populations [17]. They provide refuge
habitat to many other species, and can be alternate hosts for beneficial insects
and microflora in biocontrol tactics. In addition, their vast phenotypic biodi-
versity is valuable in its own right.
Summary
Invasive plants have significant effects on humans and cause economic, envi-
ronmental, aesthetic and biological harm to biodiversity, ecosystem function,
and human welfare. The appearance of invasive plants in terrestrial and aquat-
ic landscapes is associated with perturbations caused by human population
growth and activity. Herein is posed a conjecture that a successful plant inva-
sion is the consequence of the presence of a species possessing life history
traits suitable to exploit opportunities available at a locality. Given these two
conditions, a successful invader must disperse into, colonize and occupy that
locality for some period of time. The last requirement is that humans must per-
ceive some invasions as a problem. Without all these events occurring, a plant
is not considered invasive. Perception of a plant as invasive is a complex, often
subjective process. Inspection of public policy and reflection on human value
systems provides a more systematic method of understanding how human
activity creates selection pressure and opportunities for invaders. The human
role in creating these opportunities includes the impact of human population