Disturbance–diversity models: what do they really predict and how are they tested?

J Robin Svensson,Henrik Pavia,Mats Lindegarth,Per R Jonsson

doi:10.1098/rspb.2011.2620

Abstract

The intermediate disturbance hypothesis (IDH) and the dynamic equilibrium model (DEM) are influential theories in ecology. The IDH predicts large species numbers at intermediate levels of disturbance and the DEM predicts that the effect of disturbance depends on the level of productivity. However, various indices of diversity are considered more commonly than the predicted number of species in tests of the hypotheses. This issue reaches beyond the scientific community as the predictions of the IDH and the DEM are used in the management of national parks and reserves. In order to compare responses with disturbance among measures of biodiversity, we used two different approaches of mathematical modelling and conducted an extensive meta-analysis. Two-thirds of the surveyed studies present different results for different diversity measures. Accordingly, the meta-analysis showed a narrow range of negative quadratic regression components for richness, but not evenness. Also, the two models support the IDH and the DEM, respectively, when biodiversity is measured as species richness, but predict evenness to increase with increasing disturbance, for all levels of productivity. Consequently, studies that use compound indices of diversity should present logical arguments, a priori, to why a specific index of diversity should peak in response to disturbance.

Highlights

The well-known intermediate disturbance hypothesis (IDH) [1] and the dynamic equilibrium model (DEM) [2,3,4] together constitute an influential framework in ecological theory as well as in conservation and management [5,6]
We here show that an established model on the DEM and a new, spatially explicit model on the IDH only show the predicted patterns when biodiversity is measured as species richness
Our extensive meta-analysis of published empirical tests of the IDH is consistent with the model predictions as species richness yielded stronger hump-shaped relationships between disturbance and diversity than did evenness

Summary

INTRODUCTION

The well-known intermediate disturbance hypothesis (IDH) [1] and the dynamic equilibrium model (DEM) [2,3,4] together constitute an influential framework in ecological theory as well as in conservation and management [5,6]. Because tests of the DEM with more than two levels of disturbance that use multiple measures of diversity are not common and information on the level of productivity in studies on the IDH are rarely given, the importance of the response variable for interactive effects of disturbance and productivity could only be evaluated by the mathematical modelling. The reason for only including studies that report support for the IDH was to be able to evaluate how differences among diversity measures affect not all possible patterns between disturbance and diversity, but those that are vital for the outcome of tests of well-known hypotheses (i.e. the IDH, certain level predictions of the DEM and their related models). 60 studies included more than one measure of diversity, mainly species richness (the number of species in a community; S), Shannon’s index H 0 (equations (2.4) and (2.5); [28,29]) and evenness (equation (2.6); [27])

S ln and

Findings

DISCUSSION