Dealing with the dilution effect

The idea that there is reduced disease exposure risk in systems with high biodiversity is certainly an attractive one. Basically more species in an ecosystem ‘dilutes’ the chances of a parasite coming across a good host.  The argument follows that protecting biodiversity can have positive implications for human health. This idea however has sparked a massive amount of controversy and passionate debate  – see an excellent summary of the debate here:  the

This idea originating from a Conservation Biology paper by Ostfeld and Keesing (see the link below) on Lyme disease has been labelled everything from ‘visionary’ to a ‘fantasy’. I have mixed feeling about the paper – but I think the idea at least is an interesting one worthy of the attention that it gets. How to even conduct research to test this idea properly is contentious- in a  meeting a few years back people that have devoted their professional careers on this idea cannot come to a consensus. Adding further complexity, is that there is still  debate on how to measure biodiversity effectively in the first place (even though there have been huge advances  – See the article by Chiarucci et al below). As with most ecological research, there are also issues working at what scale to asses the effect and what species to use etc.

Unsurprisingly (if you have read my previous articles) I think that a functional and phylogenetic community ecology approach has potential to overcome some of these issues at least. What I feel is needed to answer this question appropriately  is a study design  with multiple sites across known diversity gradients at multiple scales (any ideas anyone?). This study design coupled with vertebrate surveys (rather than relying on coarse distribution data) and next-gen metagenomic  sampling symbionts/parasites from a sample of the hosts.  Using functional diversity and composition with taxonomic diversity and composition metrics of the host (and maybe the parasites?) would be useful too – and may allow for more broad applicability of the findings i.e. even though the host species composition is different the functional composition is the same.

Anyway if anyone has any ideas and may like to work on  a similar project in the future – let me know!

The original Ostfeld and Keesing paper:

Chiarucci et al diversity article:


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