Animal Contests as Evolutionary Game (pages 4 and 5)

In class we’ve been discussing the hawk-dove game, and how it relates to evolution. This article describes the Mexican spider Oecobius civitas and explains how its strange habits can be explained by an expanded version of hawk-dove evolution. The Mexican spider, unlike most species, flees from its territory and finds a new one whenever it is disturbed by an intruder. It seems counter-intuitive that a species with this kind of behavior could be evolutionarily stable. This article explains the concept of bourgeois and anti-bourgeois behavior to explain how species like the Mexican spider could have evolved from a previous “hawk”.

A Bourgeois as defined in this article is a species that will attack invaders while backing away when in the territory of another animal. This is different from a Hawk, which would attack in either situation. An Anti-Bourgeois will attack when it is in enemy territory and back off when its own territory is invaded. A good way of looking at it in terms of this class is that a Bourgeois acts as a Dove when invading and a Hawk when invaded. An Anti-Bourgeois acts as a Hawk when invading and a Dove when invaded.

Both Bourgeois and Anti-Bourgeois could prove to be more evolutionarily stable than a Hawk under certain condition. If one animal is Bourgeois in a group of Hawks, he fares the same when his own territory is under attack because he also attacks. When he is in a different territory though, by backing off, he gets a higher payoff than the Hawk if the chances of surviving are low and the probability of the owner keeping his own territory is high. However, the Mexican Spider does exactly the opposite. This spider always gives up his own territory to an intruder and enters a new territory, a behavior that doesn’t seem at all useful at first notice. However, if an Anti-Bourgeois is living among Hawks, this behavior, according to the article, could be evolutionarily stable. Payoffs are the same for an invader – both attack. The difference is in being invaded. If chances of surviving an attack are low and the probability of an owner keeping the territory isn’t much better than half, the Anti-Bourgeois fares better than the Hawk. Under these conditions, the trait is favored and is passed on. The payoffs for the Mexican Spider’s behavior allow it to be favorable despite seeming bizarre.