The Intermediate Disturbance Hypothesis (IDH)

I have made a start on some reading ahead of starting my MSc in September. I am interested in rewilding as an approach to conservation ecology. A paradigm I am currently exploring is the potential for rewilding to successfully manage abandoned farmland in Europe (blog to follow soon) and a concept that crops up in this reading is the intermediate disturbance hypothesis (IDH). I felt this interesting concept deserved its own post to discuss it ahead of a longer post on rewilding in Europe to follow.

Policy makers and researchers who argue that rewilding will have negative impacts on biodiversity cite the IDH in support of their arguments, Navarro and Pereira, (2012). The theory states that biological diversity is highest in extensively managed ecosystems where disturbance factors are moderate, Wilkinson (1999).

Essentially ecosystems are prevented from reaching communities at both ends of their succession scale (plagioclimax) therefore limiting interspecific competition and promoting biodiversity. The organisms that outcompete at the start and end of succession; pioneers and climax species, cannot dominate the system so diversity is higher. Ecologists who have supported IDH and carried out empirical tests predicted a humped relationship between species diversity and disturbance factors (Figure 1). In some studies such a relationship was indeed observed.

Figure 1 - Humped relationship between diversity and disturbance

However there is criticism of IDH. Fox (2013) states that in the vast majority of empirical cases the relationship predicted in figure 1 is not observed. It is argued that abundance of species will be impacted by moderate disturbance but not the mechanisms of interaction between species. If anything the levels of competition required between species in order to impact their populations will be reduced as a result of smaller populations and less genetic diversity, ultimately impacting communities capacity to adapt.


References

Fox, J. (2013) "The intermediate disturbance hypothesis should be abandoned". Trends in Ecology & Evolution. 28 (2) 86-92

Navarro, L. and Pereira, M. (2012) "Rewilding Abandoned Landscapes in Europe". Ecosystems. 15 900-912

Wilkinson, DM. (1999) "The disturbing history of intermediate disturbance". Oikos. 84 145-147.