The replacement series

Authors


Peter Jolliffe (fax 604-822-8640; e-mail pjoll@unixg.ubc.ca).

Summary

1 The replacement series has been used widely to assess interference, niche differentiation, resource utilization, and productivity in simple mixtures of species. Correctly used, the approach can lead to some valid interpretations. In order to avoid criticisms, however, researchers should appreciate the assumptions and limitations of this methodology.

2 A replacement series contains confounded species density treatments. Replacement series experiments therefore provide collective results and cannot distinguish separate contributions to interference by the constituents of a mixture.

3 In a replacement diagram, trends in observed yields per species can be due to a multitude of possible levels of intra- and interspecific interference. Similarly, trends in expected yields per species do not represent specific levels of intra- and interspecific interference. A replacement series is therefore unsuitable for the quantitative evaluation of interference or niche differentiation.

4 A standard replacement series, but not a proportional replacement series, may be used to detect an imbalance between intra- and interspecific interference for a component of a mixture. If competition for resources is assumed or known to be the sole cause of interference, then such experiments yield a qualitative evaluation of complementary resource utilization by the mixture components.

5 The possibility of total density dependence impedes generalization from a replacement series result. Other biases, due to initial size and time of observation, may occur with replacement series and related experimental structures.

6 Results from a replacement series are of questionable value in predicting the long-term outcome of an association between species.

7 Replacement series are a valid setting, but not the only possible setting, for some kinds of yield comparisons. These include comparing productivity of monocultures with that of simple species mixtures.

8 In some cases, interpretations obtained from replacement series have not been confirmed using other methods but, on the whole, conclusions from replacement series do not seem to be characteristically different from those obtained using other approaches.

Ancillary