Spatial scale diversity
Spatial patchiness
Population genetic and phenotypic structure
There are many aspects of spatial diversity in weed habitats. Spatial heterogeneity is complex, with many influences. It will be fully developed in the Life History section. For now, consider the spatial scale and a simple summary of factors that contribute to patchiness in fields.
Spatial Diversity of Habitats
An essential part of understanding habitats is the scale at which habitats
exist. For example, to a farmer trying to manage a field, there are very
big differences between habitats at the microsite scale and the field scale.
The farmer is most interested in scale from a practical perspective: tractor
scale and field scale. This example is the essence of site-specific crop
and field management. Are weed seedlings in the spring uniform over a field
habitat or do they exist in patches? Why?
Habitats exist at many spatial scales:
->Global
--->Continental
------>Region or State
--------->Landscape
------------>Farm
--------------->Field
------------------>Site
-------------------->Microsite
Spatial Patchiness of Habitats
Factors that cause weed patchiness in fields; factors that determine the scale of a plant's spatial diversity. Heterogeneity of:
1. resources and habitat:
environment
a.
Environment: water, flood, drainage
b. Soil: low and high spots,
soil type, seed bank distributions, fertility, OM, pH; microsites safe or not
c.
other landscape features
2.. seed dispersal patterns
a.
wind, gravity, weed seed dispersal structures
3. competition
a.
neighbors
b. biotypes within a
species adapted to different areas
4. farmer (weed manager) practices,
crop production:
a.
tillage and planting: disturbance
b. combines and harvesting
c. herbicides and cultivation
Reference: Selection in a patchy environment (Harper, 1977; pg. 774-776)
Population Genetic and Phenotypic Structure
One of the cross-cutting concepts we will explore is population genetic structure, the spatial distribution of genotypes (and phenotypes) across the landscape and around the world. It is related to biogeography, but is especially relevant to what species and variants occupy a habitat.
For some insight into one weed group, the weedy foxtails (Setaria spp.-gp.), look at the section on population genetic structure (pages 5-7) in this review paper:
Dekker, J. 2003. The foxtail (Setaria) species-group. Weed Science 51:641-646. [.pdf 7.18.03]
