Frean M, Abraham E R
School of Mathematical and Computing Sciences, Victoria University, PO Box 600,Wellington, New Zealand.
Proc Biol Sci. 2001 Jul 7;268(1474):1323-7. doi: 10.1098/rspb.2001.1670.
In the children's game of rock-scissors-paper, players each choose one of three strategies. A rock beats a pair of scissors, scissors beat a sheet of paper and paper beats a rock, so the strategies form a competitive cycle. Although cycles in competitive ability appear to be reasonably rare among terrestrial plants, they are common among marine sessile organisms and have been reported in other contexts. Here we consider a system with three species in a competitive loop and show that this simple ecology exhibits two counter-intuitive phenomena. First, the species that is least competitive is expected to have the largest population and, where there are oscillations in a finite population, to be the least likely to die out. As a consequence an apparent weakening of a species leads to an increase in its population. Second, evolution favours the most competitive individuals within a species, which leads to a decline in its population. This is analogous to the tragedy of the commons, but here, rather than leading to a collapse, the 'tragedy' acts to maintain diversity.
在儿童游戏“石头剪刀布”中，玩家各自从三种策略中选择一种。石头能赢剪刀，剪刀能赢布，布能赢石头，所以这些策略形成了一个竞争循环。尽管竞争能力的循环在陆生植物中似乎相当罕见，但在海洋固着生物中却很常见，并且在其他情境中也有报道。在这里，我们考虑一个处于竞争循环中的三种物种的系统，并表明这种简单的生态系统呈现出两种违反直觉的现象。首先，竞争力最弱的物种预计会拥有最大的种群数量，并且在有限种群存在波动的情况下，最不可能灭绝。因此，一个物种看似的衰弱会导致其种群数量增加。其次，进化有利于一个物种内最具竞争力的个体，这会导致该物种的种群数量下降。这类似于公地悲剧，但在这里，“悲剧”并非导致崩溃，而是起到维持多样性的作用。
