At ScienceDaily we learn, “Scientists Uncover an Unhealthy Herds Hypothesis” (June 24, 2011),
Biologists worldwide subscribe to the healthy herds hypothesis, the idea that predators can keep packs of prey healthy by removing the weak and the sick. This reduces the chance disease will wipe out the whole herd, but could it be that predators can also make prey populations more susceptible to other predators or even parasites? Biologists at the Georgia Institute of Technology have discovered at least one animal whose defenses against a predator make it a good target for one opportunistic parasite.
In principle, that should be no surprise; most defense strategies carry a cost, for water fleas or nations.
That’s because while growing larger keeps Daphnia [water flea] safe from Chaoborus [midge larva], it actually makes it more susceptible to a virulent yeast parasite, known as Metschnikowia. When Daphnia senses a threat from its predator and grows larger, it ends up consuming more of these parasitic yeasts than it does when normal size.When the yeast infects the crustacean, it kills it, causing the dead animal to release yeast spores as it decomposes. The larger the host, the more spores it releases back into the water to prey on other Daphnia.
If we assume design in nature, we should expect to uncover many more checks and balances of this sort. If heedless arms races worked in nature, most life forms would have died out a long time ago.
That said, is it true that most biologists worldwide subscribe to a “healthy herds” hypothesis? One that contradicts the ecological fact captured by the “unhealthy herds” story? That fitness itself can create lethal risks?
Too much bedtime reading of “Survival of the Fittest” literature perhaps? Lessons for all here.
File with: Antlers in heaven