Agriculture Reference
In-Depth Information
3.
Occurring in small but closely-spaced patches falling within the home ranges of
the consumer species.
Resource interactions
: the classification proposed by Tilman (1982) is based on
the extent to which resources are necessary for plant growth and how they interact.
In considering the relative importances of two pairs of resources (R1 and R2) and their
influences on individual plant growth, eight different outcomes may result (Figure I
.
40):
Resources may be
perfectly substitutable
: replacement of a given quantity of R1 by
a same amount of R2 does not change plant growth.
Resources are
complementary
when a given amount of the mixture of R1 and R2
gives a better growth than the same amount of R1 or R2 alone.
Resources are
antagonistic
when a mixture of the two resources gives lower growth
than the same amount of any single resource. Two resources that are totally antagonistic
are said to be switching.
Resources may also be
essential.
They are said to be interactive essential if an
optimal combination of both resources allows growth maintenance with a lower overall
consumption. If one of these resources may be replaced by the other, it is said to be
hemi-essential. Finally, they are
inhibitory
if an increase in each resource beyond a given
threshold diminishes growth. This classification does not consider only the feeding value
of resources, interactions described by Tilman integrate the costs associated in obtaining
and exploiting the resources together with their distribution patterns. The drawback of
this approach is that it limits the analysis to single pairs of resources.
