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).
doi:10.1073/pnas.1115133109
