Bay Journal

Prepare to be ticked off when messing with biodiversity

  • By Tom Horton on December 28, 2016
The healthier the diversity of the your surroundings, the healthier it is for you. (Dave Harp)

Protecting the environment is usually easier to the extent we can link it to human health concerns. The tough federal Clean Air Act, for example, has been driving the Chesapeake Bay cleanup by reducing nitrogen pollution from dirty air; but the real impetus for the law is the U.S. Environmental Protection Agency’s estimate that it’s saving more than 160,000 human lives each year.

A far tougher sell has been promoting biodiversity, by maintaining and restoring the full suite of plants and animals and natural habitats that are under assault here and globally.

Growing documentation of wild nature’s “ecosystem services” has helped: from pollution removal by oysters and wetlands, to forests’ capacity to absorb CO2 and mitigate climate change. But none of this has proved to be the big persuader for decision makers.

“But what if the loss of biodiversity made you sick…made you and your family more likely to be exposed to infectious diseases?” asks ecologist Richard Ostfeld in his groundbreaking 2011 book, Lyme Disease—The Ecology of a Complex System.

Nationally, cases of Lyme disease have tripled in the last 25 years; and it’s becoming the most common tick-borne malady in the United States. The Northeast is the epicenter, but substantial portions of the Chesapeake region are at high risk, too. It is no coincidence, Ostfeld said, that Lyme-prone areas are where human disruption of forests and other natural habitats prevail.

For more than two decades, Ostfeld and his colleagues at the Cary Institute of Ecosystem Studies in south-central New York’s Dutchess County have live-trapped hundreds of thousands of woodland mammals, and painstakingly counted the blacklegged ticks on each that transmit Lyme to humans. That often involves holding the animals — from mice to possums, squirrels to shrews — in captivity on screens over pans of water for days, until all of the ticks on them drop off to be identified.

Their work recalls terms I used to hear Bay scientists use: “the lumpers,” researchers who seek the complex, holistic view, like Ostfeld. On the other end are “the splitters,” who work the microscopic end of the spectrum, narrowly focused.

Both may arrive at valuable insights, but Ostfeld’s book shows how our tendency to find quick and simple solutions to Lyme after it emerged (in Lyme, CT) in the 1970s did us no favors.

First, it was white-tailed deer — their numbers had exploded as Lyme disease had burgeoned, and they carried vast numbers of blacklegged ticks — still misidentified as deer ticks. But years of studies couldn’t reliably correlate deer numbers and Lyme disease. Indeed, only a tiny fraction of the ticks on deer became infected with the bacteria that causes Lyme when the ticks bite humans.

Then it was white-footed mice, which did turn out to be highly effective at infecting their ticks with the Lyme bacteria. Widespread in the environment, they appear the perfect source of the problem. Chipmunks and shrews also contribute significantly, Ostfeld found.

But it turns out to be far more complicated than how many “good” transmitters of Lyme are in the woods. Just as significant is how many other species are around that attract a lot of ticks, but eat them when grooming, or just don’t infect them like the mice do.

Opossums, for example, turn out to be veritable “ecological traps” for the blacklegged tick, consuming thousands of them a week, passing on extremely few that might ever infect a human. The bottom line is that a diverse woodland community of animals contains many such traps for the ticks that otherwise might bite a mouse or chipmunk and become likely transmitters of Lyme.

Also clear is that forests fragmented and otherwise disrupted by humans clearly favor those mammals that are better Lyme transmitters. We need to think, Ostfeld said, of managing our landscapes for ecological health to promote human health. Think more like diplomats who try to understand the complexities, versus warriors who train deadly fire on the immediate threat at hand.

Most of us would still go for the simple, direct approach, hoping for a vaccine to immunize us, or a toxic chemical to neutralize mice or ticks. None of these approaches shows much near-term promise; nor would it carry the manifold other benefits of healthier forests.

The implications of biodiversity as an agent of human health, Ostfeld wrote, go well beyond Lyme disease. There is evidence, he said, for similar relationships with West Nile virus (high bird diversity dramatically decreases risk), with hantaviruses, and likely with the Zika virus.

The ecological approach to human health, like the diplomatic approach to peace, can be annoyingly slow and dizzyingly complicated. But the link is becoming clear, and making it may be the best hope for a sustainable world.

About Tom Horton

Tom Horton has written about Chesapeake Bay for more than 40 years, including eight books. He lives in Salisbury, where he is also a professor of Environmental Studies at Salisbury University.

Read more articles by Tom Horton

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Marian Whitcomb on January 04, 2017:

I wish you would have involved the plants in this article, such as invasive Barberries, Burning Bush, and Bush Honeysuckles.


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