Review Article

Pangloss revisited: a critique of the dilution effect and the biodiversity-buffers-disease paradigm

S. E. RANDOLPHa1 c1 and A. D. M. DOBSONa1a2

a1 Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK

a2 British Trust for Ornithology Scotland, Cottrell Building, University of Stirling, Stirling SFK9 4LA, UK


The twin concepts of zooprophylaxis and the dilution effect originated with vector-borne diseases (malaria), were driven forward by studies on Lyme borreliosis and have now developed into the mantra “biodiversity protects against disease”. The basic idea is that by diluting the assemblage of transmission-competent hosts with non-competent hosts, the probability of vectors feeding on transmission-competent hosts is reduced and so the abundance of infected vectors is lowered. The same principle has recently been applied to other infectious disease systems – tick-borne, insect-borne, indirectly transmitted via intermediate hosts, directly transmitted. It is claimed that the presence of extra species of various sorts, acting through a variety of distinct mechanisms, causes the prevalence of infectious agents to decrease. Examination of the theoretical and empirical evidence for this hypothesis reveals that it applies only in certain circumstances even amongst tick-borne diseases, and even less often if considering the correct metric – abundance rather than prevalence of infected vectors. Whether dilution or amplification occurs depends more on specific community composition than on biodiversity per se. We warn against raising a straw man, an untenable argument easily dismantled and dismissed. The intrinsic value of protecting biodiversity and ecosystem function outweighs this questionable utilitarian justification.

(Received October 18 2011)

(Revised December 16 2011)

(Revised January 03 2012)

(Revised January 04 2012)

(Accepted January 11 2012)

(Online publication February 16 2012)


c1 Corresponding author: Department of Zoology, South Parks Road, Oxford OX1 3PS UK. Tel: +44 1865 271241. Fax: +44 1865 271240. E-mail: