a. Weed population
shifts
1] Inter-specific
weed population shifts
2] Intra-specific
weed population shifts
a] Wild-Crop-Weed
Complexes: weedy origins and the role of crop domestication
-Origins of weeds. 1966. DeWet, J.M.J. (.pdf)
b] Non-herbicide population
shifts
c] Herbicide-induced population
shiftsb.
b. Speciation
1] Process of speciation
2] Reproductive isolating mechanisms
3] 2 dimension of evolution
4] Modes of speciation
Weedy adaptation is the consequence of weed evolution over time. Management
practices and cropping systems used by farmers leave unused resources, and
natural selection favors certain weeds to survive and kills others. Over time
weed populations in a field will change in response to these management
practices and cropping systems.
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. Over long periods of time weedy
adaptation results in evolution of that species or group of plants.
adaptation:
1: the process of adjustment of an individual organism to environmental
stress; adaptability;
2: process of evolutionary modification which results in improved survival
and reproductive efficiency;
3: any morphological, physiological, developmental or behavioral character
that enhances survival and reproductive success of an organism
Adaptation over time
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. In this section we will look at weed adaptation on
shorter time scales, as evidenced by weed population
shifts, and on longer time
scales, speciation.
