Thresholds

“I was talking with a fisherman in a bar in Anchorage…” This was the beginning of the lecture I described in the last post by Mari K. Reeves, ecologist with the U.S. Fish and Wildlife Service in Alaska.

globe bluemarblewestIn Reeves’ talk, the fisherman with whom she had been talking had a surprising analogy for “Mother Nature.” He argued that nature is not a mother, but rather a baby. Babies are resilient, he pointed out, but they need a great deal of care. While they may heal from some injuries quickly, seemingly minor trauma can have long-term consequences that may not be immediately apparent. Connecting the fisherman’s insight with her One Health perspective, Reeves showed a modified graph based on C. S. Holling’s 1973 visualization demonstrating a threshold for resilience that takes into account the accumulation of stressors. While an animal, human, or ecosystem may be able to recover from an insult readily if it is already in a relatively healthy state, recovery is more difficult when stressors accumulate.

Multiple stressors and low- level stressors can have significant impacts, but are very difficult to study. To demonstrate the effects of small, non-toxic doses of a contaminant, Reeves showed a video of an experiment in which one could see that when an uncontaminated (control) fish smells a predator, it immediately sinks to the bottom of the tank to hide. In contrast, fish exposed to minute amounts of copper seemed fine, but were not able to smell the predator signal the same way that the uncontaminated fish did. When the predator smell was released into the tank, these exposed fish did not sink to the bottom and hide, and not smelling danger, they quickly became prey.

What does this have to do with Reeve’s study of frogs? When studying stressors affecting the health of frogs, it can be difficult to pinpoint relatively small changes in their environment. However, as for the fish in the experiment above, even minute stressors such as barely measurable levels of pesticides or heavy metals can have significant impacts on frog populations, especially when combined with other stressors. As advocates of the One Health perspective have argued, this is true for other creatures as well, including humans.

The One Health Seminar Series has been organized by veterinarian/ PhD-candidate Rhea Hanselmann (http://vetmed.oregonstate.edu/one-health-seminars ).

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