In earlier posts, I told you that the “dilution effect” is a popular hypothesis in disease ecology that says that the risk of parasite infection decreases with host diversity. I also pointed out that there is caveat: disease risk is only negatively correlated with biodiversity if the hosts in the communities with low diversity are particularly good hosts (e.g., they’re good at transmitting the parasites).
Let’ s call those particularly competent/important hosts “super hosts,” because that’s what Streicker et al. (2013) called them, and the cartoon potential is awesome. What makes a host species a super host? When parasites utilize multiple host species, why should one species be better than any other? (Open access link!)
Using a combination of mathematical modeling and a field survey, Streicker et al. (2013) described three types of super hosts. Super abundant host species are just that: they’re more abundant, on average, than the other host species in the community. Super infected host species have higher prevalences of infection than other host species in the community. And super shedder host species produce more infective stages than other host species in the community. (I talked about individuals who are super shedders, like Typhoid Mary, in a different post. Here, we’re talking about species, not individuals.)
Besides the super host cartoon potential, why should we care what mechanism leads to a host species being a super host species? Streicker et al. (2013) did a great job of showing that the effectiveness of various management strategies (e.g., treating infected individuals, culling individuals) depends on the type of super host. For instance, if the key species is a super abundant host species, then untargeted control is going to be pretty useless – if you just go out and kill a bunch of individuals, you probably won’t get the infected ones. And if the key species is a super infected host species, it’s not worth spending as much time and money on diagnosing infected hosts – you should just treat/kill the ones you catch, because they’re probably infected.
There are, of course, many more cool details in the paper, and I highly recommend checking out the pretty math.
What kind of experiment would you like to see to go along with this paper?
Streicker, D.G., A. Fenton, and A.B. Pederson. 2013. Differential sources of host species heterogeneity influence the transmission and control of multihost parasites. Ecology Letters.