We've been keeping an eye on white-nose syndrome in bats for a while now. In case you haven't, it's a fungal disease that first appeared in North America around 2006. It keeps the bats from being able to hibernate comfortably, so that they keep awakening throughout the winter, thus running out of energy and starving to death before spring comes.
In infected colonies, white-nose syndrome kills something like 70% of bats. When you combine that with the gee-whiz factoids about the thousand insects that a single bat can eat in just one night's foraging, it can make you start to wonder: what happens to all the bugs when the bats that eat them die off?
One researcher, Eyal Frank, at the University of Chicago, did more than just wonder. He came up with an answer - and that answer led to more questions, and so on, leading to a recently published article in the prestigious academic journal Science.
In a nutshell, the article suggests that after white-nose syndrome causes a bat die-off in a given area... the infant mortality rate in humans goes up. On first hearing, it doesn't make any sense - but there are a few steps in between.
Spelled out, they go like this:
- White-nose syndrome causes a steep population decline in local bats.
- The local insects, free from bat predation, start attacking farm crops.
- In response to the pestilence, farmers start applying more insecticides.
- Even used according to the label, the residual toxicity of the additional insecticides leads to more infant deaths in the area.
To put numbers on these patterns, the 70% reduction in bat populations is followed by a 30% increase in pesticide applications, which is followed in turn by an 8% increase in infant mortality.
The paper doesn't conclusively prove the links it suggests, but it does document that the same sequence of events has occurred in hundreds of counties, and the explanation it proposes is plausible. It's an eye-catching demonstration of the cliché that in ecology, everything is connected - as well as an illustration of the law of unintended consequences.
The study is available online.