RUNAWAY EVOLUTION TO SELF-EXTINCTION UNDER ASYMMETRICAL COMPETITION

We analyze a popular model of the evolution of traits related to perfo rmance in exploitative competition. This model has previously been use d to explain a mechanism by which interspecific competition can cause taxon cycles. We show that purely intraspecific competition can cause evolution of extreme competitive abilities that ultimately result in e xtinction, without any influence from other species. The only change i n the model required for this outcome is the assumption of a nonnormal distribution of resources of different sizes measured on a logarithmi c scale. This suggests that taxon cycles, if they exist, may be driven by within- rather than between-species competition. Self-extinction d oes not occur when the advantage conferred by a large value of the com petitive trait (e.g., size) is relatively small, or when the carrying capacity decreases at a comparatively rapid rate with increases in tra it value. The evidence regarding these assumptions is discussed. The r esults suggest a need for more data on resource distributions and size -advantage in order to understand the evolution of competitive traits such as body size.