How We Predators Should Manage Our Prey

As a member of the world’s top predator class I take an interest in keeping my meals coming with special emphasis on farming as we don’t have sufficient of our prey species roaming wild to keep us feeling complacent. This leaves the question open as to what do other species do when it comes to securing their food supply.

The usual answer is to fight for it. Ants, though, are rather more thoughtful and have introduced farming so that they can harvest honeydew. Of course, they will fight to protect their aphid herds in the same way we will defend our cattle to ensure our milk and meat supply.

It turns out that farming, or perhaps managed hunting, is practiced out in the wild world far away from humans and state regulations. The ecologists among us theorize that predators have an effect on the diversity of prey species and will eat their favorite delicacies thus encouraging others to proliferate.

In order to test this, Ishii and Shimada set up a laboratory with two types of bruchid beetles, C chinensis and C macalatus and studied these for a while (1). Bruchid beetles munch away on crops, but they are not particularly good neighbors and C macalatus ousted all C chinensis from the lab-world in just a couple of weeks.

However, there is a wasp, A calandrae, that likes to lay her eggs in these beetles giving her young a nice fresh food source to munch through after hatching. This wasp was introduced into lab-world and she rather favored C maculatus as a host and in 20 weeks these little bruchids no longer had the advantage.

As always, things are not quite as simple as that our wasp friend had a simple preference. When lab-world was observed over time, it was clear that our wasp was having a run on one beetle and then the other causing cyclic beetle population oscillations, while managing the population nicely for her own offspring.

So it seems that even parasitizing wasps know one beetle from another and are sharp enough to manage wild populations of species that they hunt. They are sensible enough not to drive their preferred target to extinction. It is a pity that we still don’t seem to have learned the same wisdom.

Y. Ishii and M. Shimada Proc. Nat. Academy. Sci., (2012).   

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