2.25.97
Biology & Ecology
Adaptation
adapt.html
Weedy Adaptation
Weedy adaptation is the consequence of weed evolution over time. Management
practices used by farmers select certain weeds to survive, and kill others
that don't contribute to future generations. Over time weed populations
in a field will change in response to these management practices. This section
is all about these changes: adaption, evolution, selection and population
shifts.
Adaption
Weeds change over time, the weeds that produce seed are the only ones that
will endure into the future. The changes weeds undergo are called adaptation.
Adaption within a weed species-group, species or population comes about
in many ways, all of them are directly related to the management practices
they encounter and the conditions in the environment. Weedy adaptation can
be any morphological, physiological, developmental or behavioral character
that enhances survival and reproductive success of an organism. Over long
periods of time weedy adaptation results in evolution of that species or
group of plants.
Visit the:
Evolution
Weed populations are the adaptive product of long term selection in response
to forces in agroecosystems. Certain minimum conditions are required for
evolution to occur:
1. Reproduction: A parent plant produces more offspring than can normally
survive
2. Genetic variation exists in the population
3. Selection for fitness: "Fitter" phenotypes (among those variable,
excess offspring) are more likely to survive
4. Inheritance: The "fitter" traits of those phenotypes are inherited
5. Increased probability of survival of offspring possessing a particular
phenotypic characteristic
Selection
One of the most important conditions necessary for evolution to occur is
for the more fit offspring of a parent plant to survive from among the excess
offspring that parent produces. Selection pressure is imposed on these excess
offspring by the environment as well as the management practices of the
farmer growing crops in that field. The practices that result in selection
pressure include the use of herbicides, tillage, crops and crop rotations.
Weed Population Shifts
Weed population shifts are the changes in the individual organisms that
make up the population of an locality, often caused by changes in weed management
practices.
The bottom line for a farmer, and an individual field, is that because weeds
adapt they change. Those practices that controlled weeds in your field this
year probably won't provide acceptable weed control in future years. Why?
Because what you do today kills those weeds susceptible to your management
practices. The few weeds that survive today's management practices are the
parents of the weed problems you will have in the future: leaner, meaner,
better able to handle what you dish out.
This process has been going on for thousands of years. Every crop grown
by humans, in every field, in every year for the history of agriculture
has resulted in the weeds you have in your field today.
Let your clutch out and:
Weedy Adaptation in our Worst Weeds
The most important weed population shifts probably occurred long ago. The
worst weeds we have today are the winners of this selection-adaptation-evolution
process. Take a while to tour some of those very bad weeds and learn more
about what adaptations make them so successful:
Weedy Adaptation in:
Advanced Topics in Weedy Adaptation
Adaptation of weeds to conditions in agricultural fields takes place on
many time scales, from the short-term survival of a herbicide resistant
weed to a herbicide as it emerges, through the long term changes within
a genus over evolutionary time. Most of the focus in this course is appropriately
time scales important to weed management. Below are some advanced topics
in weedy adaptation on time scales longer than is probably necessary for
weed management. These sections are entirely optional, feel free to explore
them.
