Quantitative and focused research into the effects of biodiversity on ecosystem function has not yet gained momentum in MTEs. This chapter has therefore reviewed some of the imaginative ways in which ecologists in these systems have been able to interpret existing data. This has been a useful exercise, and has provided valuable insights into how that quantitative research might be conducted, and what some of the pitfalls might be.
There is evidence, at the smallest scale considered here, that species diversity can be very important in determining the way that some MTEs function, even though its influence may be limited to specific temporal or spatial windows. For instance, the diversity of soil microarthropods appear to be important in litter decomposition (Section 7.4.2), while the nitrogen economy of some fire-driven systems is dependent on the synchrony of a particular component (viz. N-fixers) in the diversity of post-fire vegetation. The latter example illustrates that the temporal dimension of diversity can be an important and very influential factor in total system function.
Another aspect of the topic is the buffering value of diversity. This has been illustrated by a model of interaction between an apparently homogeneous functional guild of post-fire reseeding plants, each with slightly different germination behaviour, and the stochastic nature of wild fires (Section 7.4.3). This intermittent function, which might be described in terms of action windows of diversity, can also be seen in the example of predatory prey systems, where niche overlap has been interpreted as varying functionally with resource availability. On a different scale, the biological invasions which are so prevalent in MTEs can be seen as agents which directly alter native patterns of diversity. It has been shown that these can produce distinct changes in important system processes (Section 7.4.8 on fynbos system shifts).
The ultimate concern of humanity about the biophysical consequences of altered diversity is the way in which it might affect our own survival. It does not yet seem that this question can be answered directly, but the current review of MTE research throws some light on the diversity and intensity of impacts that humans have imposed on the systems they exploit. !n western Australia (Section 7.4.9), for instance, landscapes that a short while ago were impressively rich in native species have been transformed over a very short period to monospecific stands of wheat. These artificial systems now seem unable to sustain basic ecosystem processes. In contrast, the Mediterranean basin has been developed by humans over millennia, and the diversity of human approaches and techniques during that period has conformed much more closely to the natural diversity and function of landscapes, apparently protecting and stabilizing their productivity for human use where mixed small-scale agriculture survives (Section 7.4.1).
It is still unclear whether in order to predict the effects of biodiversity change on ecosystem function we need a better designed set of experiments generating more data, or a paradigm shift which can provide a better understanding of ecological complexity. The work on MTEs suggests that both are probably necessary.
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