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

• Published in: Parasitology 2012-06, Vol.139 (7), p.847-863
• Main Authors: RANDOLPH, S. E., DOBSON, A. D. M.
• Format: Article
• Language: English
• Subjects: Animals; Arachnid Vectors - classification; Arachnid Vectors - physiology; Biodiversity; Biological and medical sciences; Borrelia; Borrelia burgdorferi; Borrelia burgdorferi - classification; Borrelia burgdorferi - physiology; Community composition; Ecological function; Ecosystem; Fundamental and applied biological sciences. Psychology; General aspects; General aspects and techniques. Study of several systematic groups. Models; Host-Parasite Interactions; Humans; Infectious diseases; Invertebrates; Lyme Disease - microbiology; Lyme Disease - transmission; Malaria; Mammalia; Tick-Borne Diseases - microbiology; Tick-Borne Diseases - transmission; Ticks - classification; Ticks - physiology; Vector-borne diseases; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0031-1820; 1469-8161; 1469-8161
• DOI: 10.1017/S0031182012000200

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.