Definitions:
habitat:
1: the locality, site and particular type of local environment occupied by
an organism
2: local environment
locality: the geographic position of an individual population or
collection
Habitats are constructed within the space-time matrix. A habitat is the place, the site, the locality and particular type of local
environment occupied by weeds. As an agronomist I think of habitats mostly
as crop production fields, like a field of corn early in the growing season.
In this course we will study weeds in crop fields as well as other habitats (a residential lawn, a waste field near a factory, a highway roadside,
etc.). Weeds are found everywhere, not just in corn fields. Any
place humans try to manage weeds within is any important habitat, with its own
unique set of environmental opportunities and restrictions.
Habitats are also defined by land use factors, the type and level of management of the habitat by
humans. These land use factors are closely related to disturbance, which
is discussed in detail in this unit.
One of the most important characters of a habitat is the biological
community of the locality. In agroecosystems this is often dominated
by the crop and other weeds. This aspect of Habitat will be fully
developed in the Life History section.
Spatial heterogeneity. There are many aspects of spatial diversity in weed
habitats. Spatial heterogeneity is complex, with many influences. 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. 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, include:
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)
Urban Habitat Tour (by Ted Wilson as a 517 class project)
