July 21, 2018

Meta-Analysis, Coyotes, and Lyme Disease

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Recently I had posted a link to a “study” conducted at Pepperdine University about the diet of Northeastern coyotes, compared to Western coyotes’ and a possible link to the spread and/or perpetuation of Lyme Disease in the Northeast.

On March 4, 2018, I wrote an article sharing, in part, the publisher of Maine Sportsman Magazine, Jon Lund’s, observation that the increased population of coyotes in Maine was causing an increase in Lyme Disease-carrying ticks which in turn was the cause of up-turns in the incidences of the disease. I wrote: “In the March 2018 edition, he asks, “Are Coyotes to Blame for Increase in Ticks?” His simple explanation is that the presence of an increased population of coyotes in Maine is causing a reduction in the fox population – the trickle-down effect of an increase in ticks, particularly the tick that carries Lyme disease. The reality is that coyotes compete with and kill, directly and indirectly, the red fox that is sufficiently more adept at killing the small rodents that carry and perpetuate the Deer (Lyme) tick. In an effort to mitigate what appears to be a festering and growing incidence of Lyme disease in Maine, Lund is wondering if it is time, due to the necessity of a public health risk, to make a more serious effort at reducing the coyote population.”

According to the Meta-Analysis linked to, their conclusions do not support Lund’s theory. While I only have the Abstract of the study, I can only provide what is written there. But first, let me explain something in case readers don’t know what a meta-analysis is. A meta-analysis is “a statistical analysis that combines the results of multiple scientific studies.” (Source)

In this instance, scientists simple took data from 18 different studies about coyote diet and determined that while coyotes in the Northeast readily ate more deer, they proportionately did not eat more or less small predators (like the fox that Lund claims eat the rodents that carry the Lyme tick). The Abstract states: “Our results show that deer occur significantly more in the diet of Northeastern coyotes than in the diet of Midwestern coyotes, while small mammals occur significantly less. The occurrence of rabbits, hares, birds, vegetation, and fruit do not differ significantly by region. This supports the hypothesis that Northeastern coyotes, due to their larger size and hybridization with wolves, are better adapted at hunting large prey. Although Northeastern coyotes eat fewer small mammals than Midwestern coyotes, small mammals are still a common component of the Northeastern coyote diet. Thus the abundance of Northeastern coyotes is not likely to be positively correlated to the incidence of Lyme disease.”

It’s worth pointing out a few things. Again I’ll state that I don’t have access to the full study, however, there does seem to be some degree of contradiction but that contradiction may be insignificant.

Second, it appears from this information that because the Northeastern coyote eats far more deer, due mostly in size and cross-breeding with wolves, it may be due to a bigger appetite because the animal was bigger than the Western coyote. A conclusion on my part.

Third, this information clearly states that Northeastern coyotes eat fewer small mammals than their Western counterparts, but evidently not enough to make any sort of difference.

Fourth, this study concludes that it is “not likely” fewer small mammals consumed “positively correlated to the incidence of Lyme disease.”

It would appear that this analysis has only proven that Northeastern coyotes eat more deer than Western coyotes.

There is nothing conclusive, that I can see, that the presence of an increased population of coyotes has no effect on Lyme ticks.

Do any of the studies have data that go back to a time before the “Eastern coyote” became an invasive species? Have any of these studies taken place in long enough periods of time to take into account a changing coyote diet due to changing conditions on the ground? In other words, depending on conditions on the ground, a coyotes’ diet can have large fluctuations in amount and prey diet. Are these factored in? Will a changing diet also change the incidence of Lyme disease?

There are a lot of questions that remain unanswered. Because of this meta-analysis, I wouldn’t be too quick to disregard Jon Lund’s hypothesis about the direct correlation between coyotes and Lyme disease.

What got along superbly before the invasive species arrived. I would surmise we could get along marvelously without them now.

 

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