The de Wit replacement series is a widely used technique to assess the resource use and productivity in systems with competing species (especially plants). It is also very useful to evaluate the interspecific and intraspecific competition in different species.

Intraspecific competition is the competition for a resource (or more than one) between individuals of the same species, while interspecific competition is the competition between individuals of different species.

To use the de Wit series to test the competition between two different species we need to cultivate each of the species alone (monocultures) and paired with the competing species in increased percentages. For example, if we have species A and species B one reasonable way to set up the treatments of a de Wit series would be:

通过这些治疗,我们可以评估职业ductivity (yield) of both species when grown in monocultures (first and last row of the table). Having all the intermediate treatments with different proportions of both species allows us to evaluate the intraspecific and interspecific competition.

In figure one, you can see the typical example of a de Wit series graph. At the bottom X-axis you can find the % of species A, while at the top X-axis you can find the % of species B, and at the Y-axis the yield of species A. The blue line is the 1:1 line, and it represents the point where intra and interspecific competition are EQUAL (i.e. the addition of one individual of species B disturbs species A in the same amount that the addition of another individual of species A). The red line is the data line. In this case, the line is below the 1:1 with means that the interspecific competition is bigger than the intraspecific competition. If we look at the 50%/50% data point we can see that the yield obtained is around 0.75 kg·m^-2. However, the expected yield with no competition is 1 kg·m^-2(1:1 line at the same point), which means that the competition is reducing the yield in about 25%.

Figure 1: Example of a de Wit series graph.